1. Field of the Invention
The present invention relates to the field of neuroscience and, more particularly without limitation, to a subfield of neuroprostheses for housing devices in close proximity to the brain.
2. Glossary of Terms and Useful Definitions
The term xe2x80x9celectroencephalogramxe2x80x9d (xe2x80x9cEEGxe2x80x9d) refers to voltage potentials recorded from the scalp and encompasses any recordings obtained from a source outside the dura mater. The term xe2x80x9celectrocorticogramxe2x80x9d (xe2x80x9cECoGxe2x80x9d) refers to voltage potentials recorded intracranially, e.g., directly from the cortex. xe2x80x9cEKGxe2x80x9d is an abbreviation for the term xe2x80x9celectrocardiogram,xe2x80x9d xe2x80x9cEMGxe2x80x9d for the term xe2x80x9celectromyogramxe2x80x9d which records electrical muscle activity, and xe2x80x9cEOGxe2x80x9d for the term xe2x80x9celectrooculogramxe2x80x9d which records eye movements.
The term xe2x80x9creal-timexe2x80x9d as used herein describes a system with negligible latency between input and output.
As used herein, the term xe2x80x9couter tablexe2x80x9d refers to the outer bony sheet of the skull in contact with the scalp; the term xe2x80x9cinner tablexe2x80x9d refers to the inner bony sheet of the skull in contact with the outermost brain membrane or xe2x80x9cduraxe2x80x9d; and the term xe2x80x9cdiploexe2x80x9d refers to the part of the skull between the outer table and inner table that provides nutrients and minerals necessary for developing and maintaining the skull.
3. Description of the Related Art
Humans and animals have several normal states of behavior, such as wakefulness and sleep, as well as multiple sub-states, such as attentive wakefulness and REM sleep. Abnormal states of behavior in humans and animals include reversible states, such as seizures, and progressive irreversible states, such as dementia.
Recent advances in the field of clinical neurosciences have opened a new era for the use of and need for implantable therapeutic devices. For example, the use of prostheses, for the diagnosis or treatment of neurologic illnesses, is rapidly growing and will continue to expand as new applications are found. As new technological developments take place, so does the opportunity to improve current designs or performance, decrease power requirements or cost, or minimize complications associated with chronic implantation. For instance, a device to electrically stimulate brain regions, via chronically implanted electrodes for Parkinson""s disease, has been recently approved for commercial use by the Food and Drug Administration. Implantable devices to detect and control abnormal brain states, such as epileptic seizures, are currently under development (see Osorio et al., Epilepsia 39(6):615-627, 1998).
Currently, brain devices, such as the one used for Parkinson""s disease, are implanted under the collarbones at a substantial distance from the brain. For example, the use of wires or conductors to carry a signal into or out of the brain, requires a special, time consuming procedure and careful placement of wires and connectors to avoid scalp/skin erosion, a common and serious complication which often requires removal of the device with loss of benefit to the subject. More specifically, such an approach has several significant disadvantages: (i) the long conductors for connecting the device to electrodes implanted in the brain require tunneling under the scalp and skin, thereby requiring prolonged surgical and anesthesia for installation; (ii) the tract along the conductors often becomes infected requiring, in many cases, that the conductors be explanted with consequent cessation of treatment to the subject; (iii) the conductors often erode the overlying scalp, forcing removal of the cables so that healing can take place but, at the same time, removing the means for warning of or treating impending abnormal activities; (iv) the conductors often fracture since they are subjected to torsional and other forces generated by normal head/neck movements with consequent corrective surgery to replace the faulty conductors; and (v) in the case of telemetered signals, closer proximity of the emitter to the receiver would increase fidelity of the transmitted signals and decrease power requirements, hence prolonging battery life and decreasing frequency of surgical replacement procedures.
The placement of prior art brain devices outside the skull, such as in the infraclavicular regions, is due to lack of space between the brain and the skull to position such devices and also to the inability to convert virtual into real spaces without affecting the integrity of the skull. Indeed, while the brain is closely apposed to the inner table of the skull, leaving no usable space to safely house any device, the skull has several properties that enable conversion of virtual into real space for use of the integrated ergonomic placement of devices. These properties, which have not been heretofore exploited, include:
a) sufficient wall thickness to allow housing of access systems/electronic components partially or completely within the confines of the two tables of the skull;
b) high tensile strength; and
c) semi-circular configuration allowing equal distribution of forces over its surface.
In addition, scalp tissue has the elasticity or deformability necessary for accommodation of housing devices.
Accurate and reproducible prediction of behavioral or biologic signal changes associated with abnormal brain activities has not been generally possible as such events typically occur unpredictably. This limitation has been recently overcome, making it possible to accurately predict various types of brain states, such as epileptic seizures, etc., as taught in U.S. Pat. No. 5,995,868.
Thus, what is needed is a cerebral interface system that permits spacing essential mechanisms, which perform these or other tasks in close proximity to a subject""s brain.
The present invention includes improvements for enabling simultaneous accessibility between the brain of a subject and the outside world for direct application of measures to monitor and analyze the brain activity of the subject, to predict or detect changes in such brain activity, and to allow warning, recording, preventing, and/or controlling undesirable changes in such brain activity, such as the activity changes associated with an epileptic seizure, for example.
The present inventive cerebral interface system for sensing and/or controlling normal or abnormal brain activity in a subject includes: a brain access mechanism comprising a housing mechanism configured to be spaced in a cavity formed in the subject""s skull; an attaching mechanism configured to attach the housing mechanism to the subject""s skull; a sealing mechanism configured to provide a fluid-tight seal between the housing mechanism and the subject""s skull; a control mechanism or signal processor, such as a properly programmed microprocessor, spaced within the housing mechanism; a communication mechanism, which may include one or more sensors implanted in the subject""s brain, configured to communicatingly connect the subject""s brain to the control mechanism; and a power source configured to operatively power the apparatus.
Preferably, the housing mechanism includes an inner wall having an inner surface substantially aligned with the inner table of the subject""s skull. The inner wall may include one or more ports such that a connector or connectors of the communication mechanism can extend through the port or ports into the subject""s brain. For this arrangement, the sealing mechanism may include a fluid-tight seal between the connector or connectors and the inner wall. The sealing mechanism may include a bio-compatible coating, a layer of resilient bio-compatible materials such as silicon, polyurethane, or plastic encircling the housing mechanism, etc.
The housing mechanism, which is preferably oval shaped, may include an outer wall having an outer surface that is substantially aligned with the outer table of the subject""s skull. In that event, the housing mechanism may include a flanged edge configured to be spaced in abutting engagement with an outer surface of the outer table of the subject""s skull. Alternatively, the housing mechanism may comprise an auxiliary housing portion that extends tangentially outwardly from the cavity formed in the subject""s skull. Some of the control mechanism may be spaced within the auxiliary housing portion. Preferably, the auxiliary housing portion has substantially the same profile as the subject""s skull thereunder, with the peripheral edges thereof grading into an outer surface of the subject""s skull.
The brain access mechanism may include a communication link configured to connect the control mechanism in wireless communication with an apparatus external to the subject. The control mechanism, in conjunction with the communication mechanism and the communication link, may be configured to transmit signals from the subject""s brain to the external apparatus, which may be configured to detect and predict abnormal brain activity of the subject. Further, the system may include an output mechanism, with the control mechanism, in conjunction with the communication link, configured to receive output signals from the external apparatus, and, in response to the output signals indicating such detection and/or prediction, activate the output mechanism in response thereto. Alternatively, the control mechanism, in conjunction with the communication mechanism, may be self-contained and configured to operatively detect and predict abnormal brain activity of the subject. In that event, the control mechanism may be configured, upon detecting and predicting abnormal brain activity of the subject, to operatively activate the output mechanism.
The attaching mechanism may include removable fastening means, such as one or more screws advanced into the subject""s skull. The housing mechanism, auxiliary housing portion, and preferably removable fastening means are preferably constructed of titanium.
In other words, the present invention involves the transformation of a virtual space of the skull into a real space for the safe ergonomic placement of an access system for interfacing with the brain of a subject. This access system includes a housing for encasing the components necessary for analyzing signals indicative of the subject""s brain activity state and for providing means to detect or predict changes in such brain activity state, as well as for providing means to prevent or control such changes in activity state, including treatment of abnormal states. The present invention includes, without limitation improvements in the fields of neurology, neurosurgery, bioengineering, and biocybernetics, which enable real-time analysis of biologic signals, such as those related to an EEG signal and/or an ECoG signal of a subject. Such signals are rapidly, accurately, and automatically analyzed by the present invention in order to, for example:
a) predict or detect and signal the occurrence of an abnormal brain activity, such as an epileptic seizure, in real time or essentially contemporaneously with the arrival of the EEG or ECOG signal at a signal processor;
b) predict behavioral changes typically associated with such abnormal activity;
c) download or telemeter the detection or prediction outputs to devices for warning, therapeutic interventions, and/or the storage of data; and/or
d) apply responsive measures to prevent or control such abnormal activity in the brain of a subject.
The bi-directional cerebral interface system, described herein, provides for the safe, ergonomic, cost-effective and energy efficient implantation of a housing device for automated sensing and control of changes in brain states, considerably improving the state of the art.
The principal objects and advantages of the present invention include: providing a brain access or cerebral interface mechanism mountable in a cavity formed in a subject""s skull; providing such a cerebral interface mechanism having a housing mechanism preferably constructed of titanium; providing such a cerebral interface mechanism having an auxiliary housing portion extending tangentially outwardly from such a cavity; providing such a cerebral interface mechanism having a sealing mechanism for providing a fluid-tight seal between a housing mechanism thereof and the subject""s skull; providing such a cerebral interface mechanism having a control mechanism, such as a programmed signal processor or microprocessor, spaced therein; providing such a cerebral interface mechanism having a communication mechanism for connecting a control mechanism thereof to the subject""s brain; providing such a cerebral interface mechanism having a power source; providing such a cerebral interface mechanism having an inner wall aligned substantially co-planar with the surrounding inner surface of the subject""s skull; providing such a cerebral interface mechanism having a communication link for wirelessly connecting a control mechanism thereof to external apparatus; providing such a cerebral interface mechanism having a control mechanism for activating an output mechanism; providing such a cerebral interface mechanism securable to the subject""s skull by removable fastening means; and generally providing such a cerebral interface mechanism that is effective in operation, reliable in performance, capable of long operating life, and particularly well adapted for the proposed usages thereof.
Other objects and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings, which constitute a part of this specification and wherein are set forth exemplary embodiments of the present invention to illustrate various objects and features thereof.